Electric test tube heater

ABSTRACT

An electric test tube heater has a self-supporting, freestanding electric resistance heating coil of low mass attached to and electrically insulated from a support member adjustably mounted for vertical movement on an upright stand. The coil is wound about a vertical axis and has an internal diameter larger than the outside diameter of the test tube to be heated. A clamp is also fixed to the support member and is axially aligned with the coil for holding the test tube so as to locate the lower portion thereof within the coil. A channel-shaped reflective heat shield open at the top and bottom to allow insertion of the test tube into the heater and having a vertical slot at the front to permit visual inspection of the test tube during the heating process is fixed to the support member and surrounds the coil. The support member is pivotally attached to the stand whereby the heating coil, clamp, test tube being heated and shield are all tiltable as a unit relative to the stand.

United States Patent [191 Willard et a1.

[541 ELECTRIC TEST TUBE HEATER [75] Inventors: Roland B. Willard;William J.

Walsh; John I. Larson, all of Dubuque, Iowa [73] Assignee: SybronCorporation, Rochester,

[22] Filed: Nov. 9, 1971 [21] Appl. No.: 196,905

[52] US. Cl ..219/521, 23/253 PC, 219/342,

[51] Int. Cl. ..H05b 3/00 [58] Field of Search"; ..219/520, 521, 432,

[56] References Cited UNITED STATES PATENTS 2,031,019 2/1936 Walker etal. ...2l9/433 X 1,203,406 10/1916 Redeker ..219/521 3,430,032 2/1969Morey..... .,.2l9/52l X 3,179,499 4/1965 Hampton. ...23/253 PC 2,332,94310/1943 Sobers ..23/253 PC 1,508,799 9/1924 Klett ....2l9/521 UX1,865,472 7/1932 Lamstein ...219/433 X Massinghamu", ..219/385 1 June 5,1973 2,777,043 1/1957 Duray et a1 ..219/521 1,825,406 9/1931 Lipham..219/433 X 1,717,132 6/1929 Weinmann ..219/521 UX Primary ExamirterA.Bartis Attorney--Theodore B. Roessel [57] ABSTRACT An electric test tubeheater has a self-supporting, freestanding electric resistance heatingcoil of low mass attached to and electrically insulated from a supportmember adjustably mounted for vertical movement on an upright stand. Thecoil is wound about a vertical axis and has an internal diameter largerthan the outside diameter of the test tube to be heated. A clamp is alsofixed to the support member and is axially aligned with the coil forholding the test tube so as to locate the lower portion thereof withinthe coil. A channelshaped reflective heat shield open at the top andbottom to allow insertion of the test tube into the heater and having avertical slot at the front to permit visual inspection of the test tubeduring the heating process is fixed to the support member and surroundsthe coil. The support member is pivotally attached to the stand wherebythe heating coil, clamp, testtube being heated and shield are alltiltable as a unit relative to the stand 3 Claims, 4 Drawing FiguresPATENTEDJW 51915 3.737, 627

l 38A 38B FIG. 4

INVENTORS V I I J ROLAND B. WILLARD 26 BY WILLIAM J. WALSH w JOHN LLARSON ELECTRIC TEsT TUBE HEATER BACKGROUND OF THE INVENTION The presentinvention relates to test tube heaters and more specifically to anelectric test tube heater. Electric test tube heaters, which are to someextent safer than the conventional flame heaters, are known in the art.Such electrical heaters usually consist of a resistance wire wound in aclose coil about a refractory member which forms the upright core of theheater; or such a'coil is laid in the concentric grooves on the face ofa refractory member, which forms the base of the heater. The refractorymember and its coil are located in a housing which is shaped or whichcontains means to focus the radiant heat generated by the coil on thetest tube. Another heater incorporates the heating coil into arefractory member which is formed as a cup, parabolic in shape, to focusheat onto the test tube held in the refractory cup.

One drawback of such heaters is that the relatively large mass of therefractory member results in a slow heat-up time. Another drawback isthe low efficiency resulting from attempting to focus the radiant heatgenerated by the coil on to the test tube.

In the present invention these drawbacks are overcome by utilizing aself-supporting heating element of low mass. The coils of the heatingelement are arranged so that the test tube to be heated can be loweredinto the'center of the coil. The result is both rapid heat-up and moreefficient transfer of heat to the test tube.

SUMMARY OF THE INVENTION r The present invention may be characterized inone aspect thereof, by the provision of a self-supporting electricresistance heating coil of low mass attached to and electricallyinsulated from a support stand, the coil being wound about a verticalaxis with the internal diameter of the coil being larger than theoutside diameter of the test tube to be heated; and clamp means fixed tothe support and axially aligned with the coil for holding a test tubeupright with the lower portion of the test tube extending into the coil.

OBJECTS OF THE PRESENT INVENTION One object of the present invention isto provide an electric test tube heater which has a relatively shortheat-up time and which is safe and efficient in operation. Anotherobject of the present invention is to provide an electric test tubeheater having a low mass, selfsupporting coil which can be operated froma stepdown transformer.

A further object of the present invention is to provide an; electricaltest tube heater which utilizes a selfsupporting heating coil of lowmass, the coil being woundabout avertical axis and'of sufficient size topermit the insertion of the test tube into the coil.

These and other objects, advantages and characteriz- I ing features ofthe present invention will become more apparent upon consideration ofthe following detailed description thereof, whentaken in connection withthe accompanying drawings depicting the same.

DESCRIPTION OF THE DRAWINGS I I FIG. 1 is a perspective view of theelectrical test tube heater of the present invention and its controlmeans;

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, FIG.1 shows the heater of the present .invention generally designated at10.--A-:

control means for the heater, more specifically .described herein below,including a power supply is located within a chassis 12. The heaterincludes a support member 14 which may be attached by any suitable meansto a stand 16 similar to a conventional laboratory stand. For example,as shown in FIGS. 2 and 3,

support member 14 is attached to a well known spring clamp means 18,having projections 20 which frictionally engage stand 16 to hold thesupport member at any vertically adjusted position on the stand.Preferably, support member 14 is attached to the spring clamp by a'pivotarrangement 22 (FIG. 3) so that the support member can be tiltedclockwise and counter-clockwise from the normal vertical position shownin FIG. 2.

Attached to the support and electrically insulated therefrom byinsulators 24 is a heating element 26. The heating element isself-supporting and in the form of a free-standing coil wound about avertical axis. The heating coil may be made from any of the commonlyavailable alloys for this purpose. It should be appreciated that theinternal diameter of the coil should be larger enough to accommodate thetest tube 28, which is to be heated. Since there is no intimatelyassociated refractory support for the heater into which heat can flow,the mass of the heater consists almost solely of the mass of theheating'coil. This means that the coil heats very quickly to arelatively high temperature where radiant heat is effective intransferring heat from the coil to the test tube.

Also attached to support member 14 is a clamp 30, for holding the testtube. Preferably the clamp is disposed above and in axial alignment withthe heating coil, so that the clamp may hold the test tube with thelower portion of the test tube located in the center of the heatingelement. With this arrangement, the test tube is in a position tointercept directly a large portion of the radiation from the heatingelement.

Also fixed to support member 14 is a heat shield and reflector 32. Theshield is preferably formed as a channel, open at the top and bottom,for purposes of allowing the test tube to be inserted into the heatingelement. Except for a vertical opening 34 at the front, the shieldotherwise substantially embraces the heating element. With thisarrangement radiant heat from the coil is deflected back towards thetest tube and accidental contact with the coil is prevented. The shieldthen not only acts to increase efficiency of the heater, but also offerssome degree of protection against the user burning himself by directlycontacting the heating coil. The vertical slot 34 at the front of theshield permits a visual inspection of the test tube and its contentsduring the heating process.

FIG. 4 shows the schematic of a simple power supply and control for thetest tube heater. The chassis 12 of the power supply (indicated by thedash line) contains a transformer 36 which has two taps 38 A and 38 B inthe secondary for converting normal 120 V. AC line voltage toapproximately 6 or 12 V. respectively in the secondary of thetransformer. A first switch 40 on the chassis is an on/off switch forsupplying power to the primary of the transformer. A second switch 42 onthe chassis is for selecting between the low and high taps 38A and Brespectively of the secondary. Any suitable connection such as a plug-incord generally indicated at 44 then connects the output terminals of thechassis to the input terminals of the heating coils. By this arrangementthe operator may select between applying approximately 6 orapproximately 12 V. to the heating coil depending upon the amount ofheat which is desired.

Furthermore, operating the heati or 12 V. significantly reduces the shck hazard from the heating element.

Thus it will be appreciated that the present invention accomplishes itsintended objects in providing a simple, efficient and safe electricaltest tube heater. The heater is relatively simply constructed and thefree-standing heating element of low mass has a relatively fast heatuptime. For example, the heater of the present invention is able to bringwater in a conventional size test tube to boil in less than one minute.Making the heating element free standing with coils of sufficientdiameter to accommodate test tubes permits insertion of the lowerportion of the test tube into the coil, and allows the test tube todirectly intercept radiant heat from the coil. Since the test tube islocated in the center of the heating element, the tube receives an equalamount of heat from all sides so that it is not necessary to turn thetube as with a conventional flame heater. For this reason the tube canbe clamped in position instead of being hand held, which reduces thepossibility of burns. Placing a heat reflecting shield around the coiladds to the efficiency and safety of the heat transfer. Attaching Havingthus described the invention in detail, what is:

claimed as new is:

1. An electric heater for test tubes and the like prising:

a. vertically adjustable means;

COlTlb. a support member pivotally attached to said means;

0. a free standing, self supporting electric resistance heating coilattached to and electrically insulated from said support member, saidcoil being wound about a vertical axis and having an internal diameterlarger than the outside diameter of the test tube being heated;

d. clamp means attached to said support member in axial alignment withsaid heating coil for holding a test tube extending into said coil, saidclamp, the test tube therein, said heating coil and support member allbeing tiltable as a unit about said pivot and vertically adjustablemeans; and

e. means for connecting said coil to an electric power supply.

2. An electric heater as set forth in claim 1 including a heat shieldand reflector attached to said support member and spaced about saidheating coil, said heat shield and reflector being open at the topthereof to permit insertion of a test tube into said coil.

3. An electric heater as set forth in claim 1 wherein said heat shieldis formed with a vertical slot at the front thereof for observing a testtube inserted into said coil.

1. An electric heater for test tubes and the like comprising: a.vertically adjustable means; b. a support member pivotally attached tosaid means; c. a free standing, self supporting electric resistanceheating coil attached to and electrically insulated from said supportmember, said coil being wound about a vertical axis and having aninternal diameter larger than the outside diameter of the test tubebeing heated; d. clamp means attached to said support member in axialalignment with said heating coil for holding a test tube extending intosaid coil, said clamp, the test tube therein, said heating coil andsupport member all being tiltable as a unit about said pivot andvertically adjustable means; and e. means for connecting said coil to anelectric power supply.
 2. An electric heater as set forth in claim 1including a heat shield and reflector attached to said support memberand spaced about said heating coil, said heat shield and reflector beingopen at the top thereof to permit insertion of a test tube into saidcoil.
 3. An electric heater as set forth in claim 1 wherein said heatshield is formed with a vertical slot at the front thereof for observinga test tube inserted into said coil.